In switching converters with COT (constant on-time) control, DC calibration circuits are usually used to improve the line regulation and the load regulation.
The prior DC calibration circuits usually comprise a transconductance amplifier and a capacitor. The transconductance amplifier receives a reference voltage and a sample signal and generates an error current based on the reference voltage and the sample signal. The error current flows through the capacitor and generates a calibrated reference voltage across the capacitor. In the prior DC calibration circuits, the capacitance of the capacitor should be large enough to prevent the DC calibration circuit from saturating at light load. For example, the capacitance may be 22 nF. However, a capacitor with such large capacitance is hard to fabricate in an integrated circuit. Therefore, a dedicated pin is usually needed for connection to an external capacitor. However, the more pins the integrated circuit has, the higher the cost is.